Suppose that the speed of light in a vacuum (c), instead of being a whopping 3×10⁸ m/s, was a rather sluggish 40.0 mph. How would that affect everyday life? Throughout this problem we are going to assume that c = 40.0 mph and that time dilation is in full effect. Let's start by assuming that it is fairly easy to accelerate to speeds close to 40.0 mph. We will also ignore gravity throughout this problem. Otherwise, the earth (with an escape velocity of 11 km/s) would have turned into a black hole long ago.

Now, suppose the student wishes to bring back some ice cream from the restaurant for her friends at school, but since it is such a hot day, the ice cream will melt away in the car in only 5 minutes. How fast will the student have to drive back to get the ice cream to her friends before it completely melts?